Core/shell heterostructures

Kim S, Fisher B, Eisler HJ, Bawendi M (2003) Type-11 Quantum Dots CdTe/CdSe (core/sheU) and CdSe/ZnTe(core/shell) heterostructures. J Am Chem Soc 125 11466-11467 Aharoni A, Mokaii T, Popov 1, Banin U (2006) Synthesis of InAs/CdSe/ZnSe core/ shelll/shell2 structures with bright and stable near-infrared fluorescence. J Am Chem Soc 128 257-264... 

Saha, M. S., Li, R., Cai, M., and Sun, X. Nano wire-based three-dimensional hierarchical core/shell heterostructured electrodes for high-performance proton exchange membrane fuel cells. Journal of Power Sources 2008 185 1079-1085. 

In a further extension of LCG growth, Lieber and coworkers and Yang and coworkers independently demonstrated the preparation of nanowires with structurally complex radial or axial heterostructures. Radial or core-shell heterostructure nanowires were formed by depositing layers on a core nanowire (Fig. 6A). Using this approach, homoepitaxial growth of B-doped Si shells on intrinsic Si and heteroepitaxial... 

S. Kim, B. Fisher, H.-J. Eisler, M. Bawendi, Type-11 Quantum Dots CdTe/ CdSe(Core/Shell) and CdSe/ZnTe(Core/Shell) Heterostructures. Journal of the American Chemical Society 2003,125, 11466-11467. 

Kim S, Fisher B, Eisler H-J, Bawendi MG (2003) Type-II Quantum Dots CdTe/CdSe(Core/ Shell) and CdSe/ZnTe(Core/Shell) Heterostructures. J Am Chem Soc 125 11466... 

Potential of using the pseudomorphic replacement process in order to integrate PCPs with other functional materials was also demonstrated by Zhang et al. This group synthesized core-shell heterostructures composed of vertically standing arrays of ZnO nanorods coated with ZIF-8 crystals. These novel semiconductor PCP composites are considered as promising new types of photoelectrochemical sensors with efficient molecule selectivity. ... 

Zhou XY, Tang JJ, Yang J, Xie J, Ma L-L (2013) Silicon-carbon hollow core-shell heterostructures novel anode materials for lithium ion batteries. Electrochim Acta 87 663-668... 

Goebl JA, Black RW, Puthussery J, Gibhn J, Kosel TH, Kuno M (2008) Solution-based II-VI core/shell nanowire heterostructures. J Am Chem Soc 130 14822-14833 Hoffmann MR, Martin ST, Choi W, Bahnemann DW (1995) Environmental applications of semiconductor photocatalysis. Chem Rev 95 69-96... 

The fundamental physical properties of nanowire materials can be improved even more to surpass their bulk counterpart using precisely engineered NW heterostructures. It has been recently demonstrated that Si/Ge/Si core/shell nanowires exhibit electron mobility surpassing that of state-of-the-art technology.46 Group III-V nitride core/shell NWs of multiple layers of epitaxial structures with atomically sharp interfaces have also been demonstrated with well-controlled and tunable optical and electronic properties.47,48 Together, the studies demonstrate that semiconductor nanowires represent one of the best-defined nanoscale building block classes, with well-controlled chemical composition, physical size, and superior electronic/optical properties, and therefore, that they are ideally suited for assembly of more complex functional systems. 

Lauhon, L. J. Gudiksen, M. S. Wang, D. Lieber, C. M. 2002. Epitaxial core-shell and core-multi-shell nanowire heterostructures. Nature 420 57-61. 

Composite semiconductor nanoclusters can be classified into two categories, namely, capped- and coupled-type heterostructures. The capped nanoclusters essentially have a core-shell geometry while in a coupled system two semiconductor nanoclusters are in contact with each other. The principle of charge separation in capped and coupled semiconductor systems is illustrated in Fig. 12. 

Figure 12 Principle of charge separation in semiconductor heterostructures (a) capped (or Core-Shell) geometry and (b) coupled geometry. Electrons accumulate at the conduction band (CB) of Sn02 while holes accumulate at the valence band (VB) of Ti02.

FlG. 13.8. Schematic and optical properties of the hybrid quantum-well/nanocrystal structure, (a). The structure consists of an InGaN/GaN quantum-well heterostructure with a monolayer of TOPO/TOP-capped CdSe/ZnS core/shell nanocrystals on top of it. Electron-hole pairs in the quantum well can experience nonradiative resonant transfer into nanocrystals. The nanocrystals excited by energy transfer produce emission with a wavelength determined by the nanocrystal size. (b). The emission of the quantum well (blue) spectrally overlaps with the absorption of the nanocrystals (green). For CdSe nanocrystals with 1.9 nm radius, the emission wavelength is around 575 nm (red) (from (13)). 

This approach was appUed to heterostructured seeded nanorods, both for CdSe-CdS (type I) and for ZnSe-CdS QD/QR core-shell nanocrystals. The former system was studied extensively, using a variety of optical spectroscopy methods the data acquired suggested a charge separation, where the hole is located in the QlSe core [positioned close to one end of the nanorod (NR)j and the electron extends over the CdS shell [84]. This picture is consistent with a small value of the conduction band offset, typically Ac<0.2eV, extracted from the bulk regime. However, a direct measurement of the band offsets and the consequent charge distribution in such nanocrystals is of major interest... 

Quantum dots (QDs) were developed in the early 1970s. These atomic clusters are luminescent nanometer-scale (1.5-12 nm) heterostructures, containing from a few hundred to a few thousand atoms of a semiconductor material (CdSe, CdS or InP and InAs). They can be coated with an additional semiconductor shell (e.g. zinc sulphide) to improve their optical properties such as their brightness, and the photostability of the material since, in the core-shell QDs, photobleaching effects are strongly reduced [29]. 

Ouyang and coworkers reported a synthetic route for achieving nanoscale heterostructures consisting of a metal core and monocrystalline semiconductor shell with... 

Describe a technique (widi idustrations of your experimental setup, if necessary) to syndiesize the following heterostructures. FOR EACH, describe how you control the diameter of die core and diickness of die shed, (a) a 0-D quantum dot comprised of a CdSe core and GaP died (b) a 1-D nanowire comprised of a CdSe core and GaP shell. 

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